The present invention relates to a technology effective in an application to a switching system capable of accommodating an unspecified bit rate (UBR) service together with an available bit rate (ABR) service. An available bit rate (ABR) service in an asynchronous transfer mode (ATM) network has a peak cell rate PCR declared on a terminal side and a minimum cell rate MCR, and is such that the ATM network, though incapable of sending an ATM cell at a rate exceeding the peak cell rate PCR, assures that the ATM cell be sent at the minimum cell rate MCR, and that the ATM cells are sent with the terminal selecting a rate between the peak cell rate PCR and the minimum cell rate MCR corresponding to a status of the ATM network.
In this ABR service, the terminal is notified of the status of the ATM network by use of a resource management cell (hereinafter abbreviated to an xe2x80x9cRM cellxe2x80x9d). This RM cell is sent every time a fixed number of user cells are sent, and a receiving terminal, when the RM cell arrives at the receiving terminal via the ATM network, sends this RM cell back to the transmitting terminal. AT this time, the receiving terminal writes items of bandwidth information and congestion information to the RM cell and transmits the same cell.
Then, the transmitting terminal having taken in the RM cell sent back thereto recalculates an allowed cell rate ACR, and the communications are performed at a cell rate under this allowed cell rate ACR.
As discussed above, a QOS (quality of service) is assured by avoiding a congestion under feedback control of the RM cell.
On the other hand, an UBR (unspecified bit rate) service is of such a system that flow control is conducted in a high-order layer between the transmitting terminal and the receiving terminal with respect to the bandwidth control, and a switching equipment does not get involved in this control. Hence, there might be a possibility in which a cell loss occurs due to a fluctuation in a free resource.
Incidentally, it is presumed that the method will be centered on the congestion control based on the above ABR from now on, however, the following problems are pointed out.
First, as for the ABR, the congestion control is implemented by transferring and receiving the RM cell between the terminals, and therefore the RM cell is fed back in a large loop such as: the transmitting terminalxe2x86x92the switching systemxe2x86x92the receiving terminalxe2x86x92the switching systemxe2x86x92the transmitting terminal. Consequently, there arise a problem in which a time for the control increases, and a utilizing efficiency of the system decreases. In particular, even though the data transfer within the switching system can be kept at a high speed, it impossible to increase a processing speed between terminal devices, and therefore a great number of buffers are required.
It is a primary object of the present invention, which was contrived under such circumstances, to enable feedback control to be implemented for a UBR service not originally having the feedback control by dividing a transfer route of control information through an RM cell etc for the feedback control between an external device (a terminal) and a system and between intra-system devices, reducing a control information transfer delay time with an execution of such control as to provide a loop within respective route, and performing loop control for transferring the control information within the system.
Note that Japanese Patent Application Laid-Open Publication No.9-74420 may be used with respect to the loop control between the switching system and the external device.
To accomplish the above object, according to a first aspect of the present invention, in an ATM communication line control apparatus for storing a management cell with a transmission allowed rate and making a notification thereof, a switching system comprises an individual unit connected to a transmitting terminal or a receiving terminal, and a plurality of intra-system relay devices having transmission allowed rate calculating units. In this switching system, there are separated a transfer of a management cell between the transmitting terminal or the receiving terminal and the individual unit and the transfer of the management cell between the plurality of intra-system relay devices.
There are separated the transfers of the management cells between the transmitting terminal (the receiving terminal) and the individual device and between the intra-system relay devices, whereby an allowed rate can be determined promptly without causing any delay of the determination of the transmission allowed rate due to a delayed arrival of the management cell.
According to a second aspect of the invention, the transmission allowed rate calculating unit calculates an allowed bandwidth on the basis of a cell outflow value registered in the forward management cell, makes a congestion judgement on the basis of a load observation using the number of cells received, and modifies the allowed bandwidth with a value of this judgement.
The allowed bandwidth calculated is further modified based on the congestion judgement, whereby a more accurate transmission allowed rate can be determined.